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Published May 10, 2021 | Submitted
Journal Article Open

Near-wake structure of full-scale vertical-axis wind turbines


To design and optimize arrays of vertical-axis wind turbines (VAWTs) for maximal power density and minimal wake losses, a careful consideration of the inherently three-dimensional structure of the wakes of these turbines in real operating conditions is needed. Accordingly, a new volumetric particle-tracking velocimetry method was developed to measure three-dimensional flow fields around full-scale VAWTs in field conditions. Experiments were conducted at the Field Laboratory for Optimized Wind Energy (FLOWE) in Lancaster, CA, using six cameras and artificial snow as tracer particles. Velocity and vorticity measurements were obtained for a 2 kW turbine with five straight blades and a 1 kW turbine with three helical blades, each at two distinct tip-speed ratios and at Reynolds numbers based on the rotor diameter D between 1.26×10⁶ and 1.81×10⁶. A tilted wake was observed to be induced by the helical-bladed turbine. By considering the dynamics of vortex lines shed from the rotating blades, the tilted wake was connected to the geometry of the helical blades. Furthermore, the effects of the tilted wake on a streamwise horseshoe vortex induced by the rotation of the turbine were quantified. Lastly, the implications of this dynamics for the recovery of the wake were examined. This study thus establishes a fluid-mechanical connection between the geometric features of a VAWT and the salient three-dimensional flow characteristics of its near-wake region, which can potentially inform both the design of turbines and the arrangement of turbines into highly efficient arrays.

Additional Information

© The Author(s), 2021. Published by Cambridge University Press. Received 20 December 2019; revised 30 June 2020; accepted 9 July 2020; Published online by Cambridge University Press: 05 March 2021. The authors gratefully acknowledge funding from the Gordon and Betty Moore Foundation through grant no. 2645, the National Science Foundation through grant no. FD-1802476, the Stanford University TomKat Center for Energy Sustainability and the Stanford Graduate Fellowships in Science and Engineering. The authors would also like to recognize B. Hayes and Prevailing Wind Power for managing the operation and maintenance of the FLOWE field site, and R. McMullen for assisting with the field experiments. The authors extend their thanks to Snow Business International & Snow Business Hollywood for assisting in the selection and supply of the snow machines and the snow fluid used, for providing troubleshooting during late-night experiments, for allowing extended use of their machines and for shipping a machine to Stanford for the laboratory experiments. Lastly, the authors would like to extend their appreciation to the reviewers from the Journal of Fluid Mechanics for their detailed feedback and helpful suggestions that significantly improved the presentation of this work. The authors report no conflict of interest.

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August 20, 2023
October 23, 2023